The invention relates generally to the treatment of an effluent and more particularly is concerned with the treatment of a waste solution such as acid mine drainage.
South African patent No. 95/10009 describes a separation process for separating solids from an electrolytic liquid stream wherein iron ions are released into the electrolyte from an iron electrode. The metal ions react with phosphate in the electrolyte and settle out as iron phosphate. Settling is enhanced by the coagulation and flocculation effect of the iron ions.
The aforementioned process is carried out while maintaining the pH of the electrolyte within the boundaries of 4 to 10.
It is not evident, from the specification of the aforementioned patent, in which way the pH of the solution is maintained in the indicated range and there would appear to be no control over the pH of the liquid which is discharged after settling of the iron phosphate takes place. It would also seem that the technique described in the aforementioned patent specification is only effective for the removal of phosphate in the form of iron phosphate.
Acid mine drainage solutions, and similar acidic liquors, generally contain sulphate, often in combination with phosphate. The treatment of this type of effluent poses a problem of many parts in that, ideally, the pH of the effluent should be raised to a substantially neutral level; at least the harmful contaminants such as sulphate and phosphate should be reduced to acceptably low levels; and potentially harmful base metals, which may be dissolved in the effluent, should, preferably, be removed from the effluent as part of a single treatment process.